1. Field of Invention
The present invention relates to a cloth cutting knife driving device for a sewing machine.
2. Description of the Related Art
Conventional sewing machines are capable of forming over-edge stitches and other stitches such as covering stitches. In such sewing machines, when the over edge stitches are formed on a work cloth, the cloth edge is cut during stitching by a slide movement of an upper knife and a lower knife, the upper knife being supported on an upper knife rocking arm movable up and down, and the lower knife being fixed on a machine frame. When conventional sewing machines perform the covering stitches without cloth cutting, the upper knife remains inactive. To this end, the upper knife rocking arm rotatably supports the upper knife, so that the upper knife can be in an active position, acting on the lower knife or an inactive position, rotated apart from the lower knife, so as to not cut cloth.
However, since the upper knife rocking arm interlocks with a sewing machine main shaft, the rocking arm swings during machine operation even when the upper knife is in the inactive position. In this state the rocking arm of the conventional sewing machine is not only hazardous but also obstructive. Specifically, the sewing machine obstructs a user during operation, thus cutting down the usable work area.
In order for the upper knife rocking arm to stop swinging during operation without cloth cutting, some upper knife release devices have been developed, for example as disclosed in U.S. Pat. No. 5,427,041. In such release devices, the rocking arm stops swinging because its connection to the main shaft is released.
In one embodiment of U.S. Pat. No. 5,427,041, a greater number of elements are used for releasing the connection between the rocking arm and the main shaft. This aspect contributes to increased play at the upper knife portion and higher cost of the device.
In prior art embodiment illustrated in FIG. 8, the upper knife releasing device has an upper knife driving arm 122 for converting the rotating motion of a main shaft 118 into a rocking motion, an upper knife drive(rocking) shaft 124 rotatably supported on a machine frame to be swung by the driving arm 122. The upper knife releasing device also includes an upper knife rocking arm 116 which is rotatably supported on the drive shaft 124 at one end, an upper knife 138 at the other end, and an upper knife driving plate 126 which is rotatably supported on the drive shaft 124 at one end and has an end hole 126b at the other end. The one end of the driving plate 126 is fixed to the driving arm 122. In this structure the rotation of the main shaft 118 causes the driving arm 122 and the driving plate 126 to rotate about the drive shaft 124, which causes the other end of the driving plate 126 to swing up and down.
At the other end of the rocking arm 116, a coupling pin 148 is provided, being supported by a coupling pin tightening screw 162, so as to fit into the end hole 126b on the driving plate 126. With the above setup, the up and down swinging of the other end of the driving plate 126 causes the upper-knife rocking arm 116 to rotate about the drive shaft 124 and drive the upper knife 138 up and down. Thus, the drive shaft 124 is coupled to the rocking arm 116. When the knife 138 is to be released, the coupling pin 148 is disengaged from the end hole 126b with the tightening screw 162 loosened, allowing the driving arm 116 to be released from the drive shaft 124.
In this device, the driving plate 126 is disposed at the front portion of the inside of the machine frame, and protrudes further forward than the other parts provided inside the machine frame. Therefore, the driving plate 126 has to be extended outside an outer casing, (cover) 114 covering the front of the frame, through an opening on the cover. Alternately, it may be accommodated inside, if the cover is expanded. Also, coupling pin 148 has to be extended through an opening formed on the cover.
In the event that the cover has an opening, exposing the driving plate 126 through the opening is dangerous. Therefore, additional covering structure for the plate 126 is needed. Neither providing the additional covering nor expanding the cover is preferable from the design viewpoint.
In accordance with the present invention a knife driving device for cutting cloth in a sewing machine is provided. In one embodiment, the cloth cutting knife driving device in which an upper knife rocking arm interlocks with a sewing machine main shaft and can be released in an embodiment with fewer parts.
An object of the present invention involves providing a cloth cutting knife driving device having a structure that does negatively influence the aesthetics or manufacturability of a machine case.
A further object of the invention is to provide a cloth cutting knife driving device with excellent operability.
The present invention provides for a cloth cutting knife driving device. The device includes a drive shaft, which is able to swing rotatably, by interlocking with a main shaft. The device further includes a rocking arm rotatably supported on the drive shaft at the distal end for rocking motion, and a cloth cutting knife supported at the distal end of the rocking arm so as to be rigidly held in a cloth cutting position or an inactive position. The device may move up and down through the rocking motion of the rocking arm. The device has a coupled state and a released state for the drive shaft and the rocking arm, both states are brought about by an engaging part on the drive shaft and a movable member, movable with respect to the rocking arm in a direction perpendicular to an axial direction of the drive shaft. The coupled state is brought about by engaging the movable member with the engaging part, with the movement of the movable member in its axial direction toward one side. Whereas, the released state is achieved by releasing the movable member from the engage part with the movement of the movable member toward the other side. In a particular arrangement, the engaging part is a hole formed on the drive shaft, and the movable member is a pin with a tip at one end.
In one embodiment, the movable member and the engaging part are arranged inside the rocking arm, and the device further includes an operation member (15) for operating the movable member from outside the rocking arm. The present invention further includes a spring means mounted on the rocking arm for holding the movable member in the coupling state and the released state.
Advantageously, the device further includes positioning members for regulating the position where the movable member can engage with the engaging part when the coupling state is to be made. The device may include a spring member fixed on the machine frame for holding the operation member when the rocking arm is lifted up in the released state.